Optoelectronic devices employing fibers for light collection and emission

ABSTRACT

An optoelectronic device, such as a solar cell, light-emitting device, or photodetector, comprises a substrate, a number of fibers supported by the substrate so that an end of each fiber is in electrical communication with the substrate surface; an optional first layer, covering the substrate, though which the fibers protrude, and a second layer overlaid on at least part of the first layer and exposed fiber surfaces. The second layer may be electrically conducting, and electrically isolated from the substrate surface by the first layer. The second layer can be in electrical communication with each fiber, and an electrically conducting path can exists between the second layer and the substrate surface through each fiber. The substrate, in whole or in part (such as the substrate surface) can be electrically conducting. The electrically conducting path may comprises a semiconductor p-n junction, so that the optoelectronic device emits light, provides a photovoltaic potential, and/or is sensitive to light, for example acting as a photoresistor, photodetector, and the like.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/315,723, filed Dec. 12, 2002, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to improved solar collectors and other devicesusing one or more substrates supporting a plurality of fibers appliedusing flocking techniques.

BACKGROUND OF THE INVENTION

The goal of solar energy as an inexpensive, alternative energy sourcehas been a dream for many years, and on occasion that dream seemselusive. Various techniques have been attempted and patented to increaseefficiency, including multi-bandgap, tandem and compound cells.Experiments have also been tried with respect to physical structures,including concentrators and non-planar collection surfaces.

A search of the prior art was undertaken, and the following referenceswere identified, all of which are incorporated herein by reference:

U.S. Pat. No. 3,780,722 to Swet describes a fiber optical solarreceiver, comprising a boule of fibers shaped into an actuate collectingsurface at one end.

U.S. Pat. No. 4,117,829 to Gross et al. discloses a heat-absorbingsurface having a multiplicity of substantially parallel fibers securedto the surface.

U.S. Pat. No. 4,252,865 to Gilbert et al. discloses a highlysolar-energy absorbing device wherein the surface exposed to incidentsolar energy is an amorphous semiconductor material having particularlycharacterized roughness.

U.S. Pat. No. 4,322,571 to Stanbery discloses solar cells withinter-electrode photoactive regions preferably being texturized, therebyoptimizing current generation per unit of incident radiation andminimizing reflection losses.

U.S. Pat. No. 4,353,788 to Jeffrey et al. discloses a method ofpreparing amorphous silicon monohydride using sputtering.

U.S. Pat. No. 4,409,423 to Holt discloses a solar cell which comprises athin silicon chip having on one surface a plurality of holes, closelyspaced in a desired array, the walls of the holes defining the verticaljunction of the cell.

U.S. Pat. No. 4,478,209 to Guarnieri discloses a radiant energycollector having a substrate coated with polyimide which has beensurface-textured to impart the coated substrate with high absorption andlow emissivity for radiant energy.

U.S. Pat. No. 4,555,622 to Glass et al. discloses a photodetector havinga substantially periodic surface.

U.S. Pat. No. 4,663,188 to Kane discloses a photoconductor including alight transmissive electrically conducting layer having a texturedsurface with a semiconductor body thereon.

U.S. Pat. No. 4,812,352 to Debe discloses a substrate bearing on atleast one major surface thereof a microlayer comprising an array ofdiscrete, single- or poly-crystalline, uniformly oriented (with respectto the substrate surface) microstructures of a solid, organic material.

U.S. Pat. No. 4,931,412 to Fischer et al. discloses a thin film solarcell with an n-i-p structure has roughened substrate surface.

U.S. Pat. No. 5,039,561 to Debe discloses a substrate bearing amicrolayer which comprises uniformly oriented, crystalline, solid,organic microstructures.

U.S. Pat. No. 5,081,049 to Green et al. provides a method of processinga silicon solar cell substrate, by scribing the surface of the substrateto form a plurality of recesses and subsequently chemically etching thepatterned surface to give a plurality of discreet upstanding structuresof specifically desired shape.

U.S. Pat. No. 5,816,238 to Burns et al. discloses a solar collectorexhibiting durable fluorescent properties comprising a polymeric matrix,dye, and hindered amine light stabilizer.

U.S. Pat. No. 6,224,016 discloses a flexible solar cell having aflexible substrate.

Despite these advances, the prior art fails to disclose optoelectronicdevices, such as solar cells, light emitting devices, andphotodetectors, comprising a plurality of fibers adhered to alight-emitting or light-receiving surface.

SUMMARY OF THE INVENTION

An optoelectronic device, such as a photovoltaic device (such as a solarcell), light-emitting device, photodetector, or photoresistor accordingto the invention comprises a substrate, having a substrate surface, aplurality of fibers supported by the substrate surface, a first layer,located so as to cover at least part of the substrate surface and atleast part of the plurality of fibers, a second layer, located so as tocover at least part of the first layer, a first electrical contact inelectrical communication with the first layer, and a second electricalcontact in electrical communication with the substrate or first layer.

In a photovoltaic device, an electrical potential can be obtainedbetween the pair of electrical contacts on exposure of the device tolight. The first layer, second layer, and/or fibers may comprise aphotovoltaic material providing a separation of electrical charges whenilluminated. The first layer, second layer, and/or fibers may comprise asemiconductor material (such as an organic or inorganic semiconductor),a charge separation material, a polymer or polymer blend, a conductingpolymer, a blend of a conducting polymer with a plurality of inorganicsemiconductor particles, for example, a blend of poly(3-hexylthiophene)and cadmium selenide. The second layer, and/or substrate surface maycomprise a conducting polymer, conducting metal oxide, metal film, orother conducting material, and may be transparent.

In a light emitting device, light emission can be obtained from thedevice on passage of an electrical current between the pair ofelectrical contacts. The first layer, second layer, or fibers maycomprise a light emitting material, such as a light emitting polymer.

In addition, light emission or photovoltaic effects may be generated atinterfaces within the device, for example between the first layer andthe second layer, between the fiber and the substrate, between the fiberand the first layer, between fiber components of a multi-componentfiber, or from some other interface. Fibers or layers may compriseinternal semiconductor p-n junctions.

An optoelectronic device can comprise a substrate, a number of fiberssupported by the substrate so that an end of each fiber is in electricalcommunication with the substrate surface; an insulating layer, coveringthe substrate, though which the fibers protrude, and a conducting layer,electrically isolated from the substrate surface by the insulatinglayer, wherein the conducting layer is in electrical communication witheach fiber, and an electrically conducting path exists between theconducting layer and the substrate surface through each fiber. Thesubstrate, in whole or in part (such as the substrate surface) may beelectrically conducting. The insulating layer may be omitted. Theelectrically conducting path may comprise a semiconductor p-n junction,so that the optoelectronic device emits light, provides a photovoltaicpotential, and/or is sensitive to light.

A light emitting device can be energized by an electric current passingthrough at least part of each fiber. For example, electrical contactsmay be provided on the device, in electrical communication with thesubstrate and a conducting layer, through which an electrical currentcan be applied. Light may be emitted from a p-n junction on providingelectrical communication between the conducting path through the fiberand a source of electrical energy. Electromagnetic radiation (such aslaser radiation, microwaves, radio waves, UV, or IR), or other radiationsuch a nuclear radiation, sound waves, or ultrasound, may also be usedto excite emission of light, for example through inducing current flowthrough a conducting path.

Alternatinng currents may be used to energize a light emitting layer orfiber even without direct (conductive) electrical communication, forexample using capacitive or inductive coupling.

In other embodiments, such as a solar cell, an electrical potential maybe provided between the substrate and conducting layer on exposure ofthe fibers to emit visible or invisible optical radiation.

An adhesive layer can be provided to hold the fibers on the substratesurface. The fibers can be randomly deposited on the substrate surfaceby a flocking method. The fibers can comprise a semiconductor material,metal, polymer, electroluminescent material, insulator, conductor, orother material or combination of materials. Fibers may comprise asemiconductor p-n junction, concentric layers of material, or otherstructure.

A p-n semiconductor junction can formed at the interface between thefibers and the substrate surface, within the fibers (for example bydoping before or after a flocking procedure), or at the interfacebetween the fibers and a conducting layer deposited over the fibers.

A photovoltaic device (such as a conventional silicon based solar cell)may comprise a substrate of semiconductor material (such as silicon)comprising a p-doped region and an n-doped region, a p-n semiconductorjunction between the p-doped region and the n-doped region, and asurface, wherein an electrical potential is developed between thep-doped region and the n-doped region on illumination of the surface.The device can further comprise a pair electrical contacts, to then-doped region and to the p-doped region respectively, so as to allow anelectrical current to be obtained from the device on illumination of thedevice. An improved device further comprises a plurality of fibersdisposed on the surface. For example, fibers transparent to solarradiation may be deposited by a flocking method on a light receivingsurface of a solar cell. The fibers may comprise a polymer, glass, afluorescent material, a light absorbing material, a UV absorbingmaterial (for example, so as to reduce aging), or other advantageouscomponent.

The fibers can be disposed on a surface of a semiconductor materialusing a flocking method, so that, for example, the fibers are randomlydistributed and are disposed so that the long axes of the fibers are, onaverage, oriented substantially orthogonal to the semiconductor surface.If the surface is textured, fibers may be substantially parallel, orsubstantially orthogonal to the local surface orientation.

The surface of the semiconductor material may supports a protectivefilm, which may be a transparent within the wavelength range at whichthe photovoltaic effect is obtained. The protective film may comprise anelectrode, forming an electrical contact. The fibers may be disposed onthe protective film. The surface may support a layer of adhesive to holdthe fibers proximate to the surface.

A photothermal system comprises a tube having an outer surface and anaperture in which a fluid can be located (for example, stored in,contained, or passed through), a layer of adhesive on the outer surfaceof the tube, and a plurality of fibers disposed on the outer surface ofthe tube, held in place by the layer of adhesive. The fibers may bedeposited on the surface using a flocking method. The tube may berotated as fibers are deposited by flocking. A film may be coated withfibers using a flocking method, and the film wrapped around the tube. Alight absorbing layer may also be provided on the outer surface of thetube. The fibers may contain a light absorbing material.

The tube may in part have a sinuous form, be supported on a rooftop, becoated with a transparent protective material, be covered with aprotective sheet, such as a glass or polymethylmethacrylate sheet, andthe like. The tube is mounted on any surface exposed to sunlight, andprotected from mechanical damage by a protective sheet mounted above thetube (between the tube and the source of solar radiation).

Water, or other fluid, can be pumped through the aperture of the tube soas to be warmed by solar radiation. Pumping can be continuous, orintermittent. Water may circulate through the tube once, or more thanonce. Water may be sterilized by heating alone, or by heating combinedwith another treatment, such as chlorination, or UV exposure.

A light-emitting system according to the invention comprises a substratehaving a substrate surface, a plurality of fibers supported held on thesubstrate surface by a layer of adhesive, and a source of energy,wherein the source of energy induces a light emission from the fibers.The source of energy may comprise electromagnetic radiation (such as alaser, radio waves, microwaves, IR, visible, UV, x-ray or gamma rays),an electric potential, an electric discharge, a plasma, capacitive orinductive coupling to an alternating current source, ultrasound, orother source of energy. The fibers may comprise an electroluminescentmaterial, or other light-emitting material.

A method of fabricating a photovoltaic device comprises, providing anelectrically conducting substrate (for example, the substrate may have aconducting surface), coating the substrate with an adhesive layer, anddepositing a plurality of fibers on to the substrate, for example usinga flocking method. Flocking methods include electrostatic flocking,pneumatic flocking, vibration flocking, gravity fed flocking, and acombination of all or some of these techniques. The fibers may extendaway from the substrate, and can be held in place by an end of eachfiber by the adhesive layer. In one embodiment, the fibers comprise asemiconductor material, and are treated so as to obtain a p-nsemiconductor junction within the fibers. Electrical contacts areprovided to the fibers, so that an electrical potential is obtainedbetween the electrical contacts on exposure of the fibers to light. Forexample, a p-n semiconductor junction can be obtained within the fibersby diffusion of one or more dopants into the fibers (before and/or afterdeposition of the fibers onto the surface).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an optoelectronic device having a plurality of fibers;

FIGS. 2A and 2B shows a fiber having an internal p-n junction;

FIG. 3 illustrates a method of fabricating an improved optoelectronicdevice;

FIG. 4 shows a photovoltaic device having a plurality of opticallytransmissive fibers;

FIG. 5 shows a photothermal collector;

FIG. 6 shows a solar heating system for a fluid;

FIG. 7 shows an optoelectronic device;

FIG. 8 shows an optoelectronic device;

FIG. 9 illustrates a method of optically exciting fibers;

FIGS. 10 and 11 show configurations having opposing substrates;

FIG. 12 illustrates a textured substrate;

FIG. 13 illustrates successive flocked layers;

FIG. 14 shows a device formed using a luminescent polymer; and

FIG. 15 shows an optoelectronic device.

DEFINITIONS

In this specification, the term fiber refers to rods, tubes, ellipsoids,whiskers, tendrils and similar elongated structures having a finitelength and a cross-sectional dimension less than the length.

Flocking refers to the coating of at least part of a surface with aplurality of fibers. Various flocking techniques are known in the art,all of which apply fibers in a substantially random fashion.

A substrate acts a support for the fibers. Unless stated otherwise, theterm “substrate surface” refers to a surface of the substrate on whichfibers are deposited, in whole or in part.

The distal end of a fiber is the end protruding away from a surface. Theproximate end of a fiber is the end in contact with, or most proximateto, the substrate surface.

A flock adhesive can be used to promote adherence of fibers to asurface. Flock adhesives may comprise silicone, acrylate, urethane,acrylonitrile and other adhesives known in the art, UV curableadhesives, and also other liquids and gels which may be used to holdfibers at the substrate surface.

An optoelectronic device may be a light-emitting device (such as a lightemitting diode or laser), photovoltaic device (such as a solar cell),and the like, for example emitting or sensitive to IR, optical, or UVradiation, or a photodetector.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-section of part of an optoelectronic device, showngenerally at 10, comprising an electrically conducting substrate 12, anadhesive layer 14, insulating layer 16, fiber 18, an electricallyconducting layer 20, a first electrical contact 24, and a secondelectrical contact 26.

The fibers can be deposited on the substrate by a flocking technique, sothat adhesive layer 14 is a flock adhesive layer. Flocking techniquesare well known in the art, as discussed in more detail later.

For example, the conducting layer 20 may comprise a p-type dopedsemiconductor, and the fibers may comprise a n-type doped semiconductorso as to form a p-n semiconductor junction at the interface 22 betweenthe conducting layer and the fiber surfaces. As will be clear to thoseskilled in the art, the doping pattern can be reversed (i.e. theconducting layer may comprise an p-type doped semiconductor and thefibers comprise an n-type doped semiconductor). It can be advantageous,for photovoltaic applications, to provide a p-n junction near thesurface of the device, and to provide a surface structure having a lowreflectance.

Illumination of the device 10 by photons can induce an electricalpotential between the conducting layer and the conducting substrate, dueto the photoexcitation of current carriers which pass through the p-njunction. The electrical potential appears between electrical contacts24 and 26.

In another embodiment, an improved light emitting diode is provided bypassing an electric current through the device (between contacts 24 and26) induces photon emission from the p-n junction. Barrier layers (forcurrent carriers such as holes and electrons) can be provided atcontact, electrode, layer surfaces, fiber surfaces, or at othersurfaces, for advantages such as increased efficiency or longer devicelifetimes.

The substrate surface may be patterned, so as to influence the spatialdistribution of fibers on the surface. For example, the substratesurface may have a plurality of depressions (for example, having across-section similar to that of the fibers), trenches, protrusions,sinusoidal or other periodicity in one or more directions, and the like.

The electrically conducting substrate and/or conducting film maycomprise a doped semiconductor, metal (such as gold, palladium, silver,or other metal film or multilayer), conducting oxide (such as tin oxide,indium tin oxide), conducting polymer, and the like. Preferably, eitherthe conducting film or substrate is at least partly transparent withinan appropriate wavelength range. Here, the appropriate wavelength rangefor a photovoltaic device is the range of wavelengths which excite anelectrical potential, and for a light emitting device it is the range ofwavelengths emitted due to electrical excitation. For an opticallyexcited light emitting device, the substrate may be transparent toexcitation light and the conducting layer transparent to emitted light,or vice versa. Alternatively, the conducting layer may cover only afraction of the exposed fibers, so as to allow light to be emitted orreceived even if the conducting layer is opaque at the relevantwavelengths.

The substrate surface may have an antireflective coating, for example anabsorbing dye, or one or more dielectric layers of thickness adapted toprovide destructive interference of reflected light, such as a magnesiumfluoride film.

The flock adhesive 14 may be electrically conducting or insulating. Forexample, the insulating layer may be formed from flock adhesive, throughwhich the fibers protrude so as to make physical and electrical contactwith the substrate surface. In this example, layers 14 and 16 arecombined into a single insulating layer. Alternatively, the flockadhesive 14 may be insulating, and an additional insulating layer 16provided, the fibers protruding through both layers so as to makeelectrical contact with the substrate. Alternatively, the flock adhesive14 may be conducting to assist electrical contact between the fiber andthe substrate. The adhesive may bead around fibers, be removed fromexposed substrate surface areas, or otherwise be non-uniformlydistributed.

Exposed flock adhesive may be removed after the flocking process iscomplete, for example to facilitate deposition of an insulating layer onthe exposed substrate surface. In this case, the layer 14 can removed,e.g. by etching, mechanical methods, thermal methods, laser ablation, orthe like, before deposition of the insulating layer 16.

After the flocking process is complete, but before the flock adhesivehas hardened, the distal ends of the fibers may be subject to a physicalforce so as to promote electrical contact with the substrate through theflock adhesive. Flock adhesive may be curable, for example using UVradiation, heat, chemical interactions, the passage of time, or somecombination of factors. Flock adhesive may be a contact adhesive. Flockadhesive may be a liquid film, which supports the fibers using capillaryforces, before removal, conversion into a permanent layer, other layerprovision, or other process.

Deposition of the insulating layer 16 may cause unwanted deposits on thefibers, particularly at the distal end. These deposits may be removedfrom the distal end of the fibers and from surrounding regions of thefibers, by methods such as dipping in etchant, flexing the fibers,mechanical abrasion, and the like, or substantially prevented fromforming by a prior surface treatment of the fibers. Alternatively, theinsulating layer deposits may allowed to remain.

The conducting layer 20 need not cover the entire surface of the fiberexposed above the insulating layer. For example, the conducting layermay only contact the side surface of the fibers adjacent to theinsulating layer. Evaporated metal films may be used, such as silver,gold, palladium, copper, or other metal film. Screen printing can alsobe used to deposit conducting films, e.g. a silver conducting film.Evaporation may be at a normal or oblique incidence. Other methods ofproviding a conducting film or its equivalent are discussed in moredetail below.

In other embodiments, the fibers and conducting layer may have the samedoping, such as p-type, and the substrate comprises an oppositely doped(n-type) semiconductor, so that a p-n junction is formed at theinterfaces between the fibers and the substrate.

In other embodiments, an optoelectronic device may be formed having ap-doped semiconductor—intrinsic layer—p-doped semiconductor (p-i-n)structure. For example, a doped semiconductor substrate may be coatedwith an intrinsic semiconductor layer, and doped fibers flocked thereon.

In other embodiments, a hole accepting organic material, such as apolymer, may be used in place of a p-typed doped semiconductor, and anelectron accepting organic material may be used in place of an n-typedoped semiconductor.

Semiconductors which may be used for substrates and/or fibers includeinorganic semiconductors (such as arsenides (e.g. GaAs, (In,Ga)As,InAs), phosphides (e.g. GaP, InP, (In,Ga)P), arsenide phosphides,nitrides (e.g. GaN, (Ga,In)N, InN), tellurides (e.g. CdTe, ZnTe,(Hg,Cd)Te), selenides (e.g. ZnSe, Cu₂Se), sulfides (e.g. CdS, Cu₂S,ZnS), selenide sulfides, silicon, germanium, magnetic semiconductors,and the like, and organic semiconductors such as polymers or otherorganic materials. Other semiconductor materials are well known to thoseskilled in the art, for example as recited in U.S. Pat. No. 6,441,395 toYu et al., the contents of which are incorporated herein by reference,and the given examples are not intended to be limiting. Fibers andsubstrate may be comprised of dissimilar semiconductor materials. Fibersmay comprise a core of one material, with a surrounding region of adissimilar material. For example, silicon fibers may be formed bygrinding, cutting, etching, laser ablating, or otherwise processingsilicon, or by crystal growth methods. Etching includes wet etching anddry etching methods, such as reactive ion etching and plasma etching.Other types of fibers may be formed by analogous methods.

Fibers may be small enough to generate quantum size effects. Forexample, silicon fibers may be used having a nanometer scale ormicrometer scale size so as to increase luminescence in the visibleregion of the spectrum, an effect well known in the porous silicon art,for example.

In another embodiment, the fibers comprise an electroluminescent polymerwhich emits light on application of an electric potential between thecontacts. The fibers may also comprise luminescent polymers which emitlight on excitation with photons.

Electroluminescent polymers, other light emitting polymers, andconducting polymers include poly(p-phenylene vinylene) (PPV),polypyrroles, polyarylenes, anthracene containing polymers,flourene-containing polymers, co-polymers, other conjugated polymers,other polymers known in the art, derivatives, co-polymers, and blends.

In other embodiments, the conducting layer can be replaced by a networkof fine conductors (such as fine metal wires, conducting polymerthreads, or the like), which may be threaded or otherwise disposedbetween and/or around the fibers.

In other embodiments, the conducting layer can comprise a conductingfluid which fills the gaps between the fibers, and is in electricalcommunication with an electrode or other electrical contact. Forexample, an indium tin oxide electrode on a glass cover may be supportedabove the fibers, and the gap filled with a conducting fluid.

Flocking methods are well known in the art. For example, electrostaticflocking or electroflocking is used to coat a surface with fibers byproviding an electrical charge on the surface, and an oppositeelectrical charge on the fibers. Pneumatic flocking uses an fluid jet toalign fibers in the direction of fluid flow. Different flockingtechniques can be used in combination, for example it is known tocombine pneumatic flocking and electrostatic flocking techniques. Fibersmay also be deposited on a surface using injection or insertion moldingmethods. Flocking methods and flock adhesives are described in U.S. Pat.No. 6,306,498, and U.S. Application Publication No. 2002/0019645, thecontents of which are incorporated herein by reference.

FIG. 2A shows (in cross-section) a fiber shown generally at 40, having astructure comprising an n-doped semiconductor cylindrical core 42, asurrounding concentric p-doped semiconductor region 44, and an outerinsulating shell 46. The fiber contacts a surface 50, having anindentation 48, and having electrical conductors 54 and 56 which contactthe n and p doped regions respectively. The substrate surface 50 hasindentations 48 which are similar in cross-section to that of thefibers. The distal end of the fiber can be coated with a protectivelayer, such as an insulating oxide.

Electrostatic flocking can be used to draw the fibers into the surfaceindentations. Flock adhesive may be restricted to the inside surfaces ofthe indentations, so that fibers not seated in an indentation are easilyremovable. Electrodes contacting the p-type and n-type regions(respectively) can be electrically interconnected. The indentation 48may be a depression having a cross section similar to that of the fiber,or may be a trench, groove, or the like.

FIG. 2B shows a top view of a fiber 60, having an n-doped core 64 andp-doped surround 62, supported by a substrate surface 76 havingelectrodes 66 and 68 protruding from conducting tracks 70 and 72. Anadjacent, similar fiber is shown at 74.

FIG. 3 (A-D) illustrates a method of fabricating an improvedoptoelectronic device. FIG. 3A corresponds to the provision of anelectrically conducting substrate 80 coated with a flock adhesive layer82. The flock adhesive can be a liquid or gel through which fibers maypass, and which serves to hold the fibers in place, at leasttemporarily. FIG. 3B corresponds to the deposition of a plurality ofsemiconducting fibers, such as fiber 84, onto the surface of thesubstrate 80. Deposition can use conventional flocking methods, as arewell known in the art. After fiber deposition, mechanical pressure orother techniques can then be used to obtain a better contact between thefibers an the surface. The flock adhesive can be curable, or otherwiseprocessed or modified, for example to provide an insulating layer suchas an oxide layer.

For example, the substrate surface may be spin-coated with a liquidsilane, such as tetraethoxysilane (TEOS). This liquid layer can be usedas a flock adhesive, to hold fibers on the substrate. Viscositymodifying additives can be used.

Semiconductor fibers can used, and be doped n-type or p-type. Fornon-limiting definiteness, in this example the fibers are assumed to bep-type doped silicon. A TEOS layer can be provided as a flock adhesivelayer 82, and after fiber deposition (for example, as shown in FIG. 3C,showing fiber 84) be converted to a silicon dioxide layer, e.g. byheating. Other silicon dioxide, ormosil, or other insulating layerprecursor may be used instead of TEOS.

The fibers can then doped with an n-type dopant, for example as shown inFIG. 3C) so that the n-type dopant diffuses into the surface of thefibers. A p-n junction is hence formed near the surface of the fibers,in this example between n-doped fiber regions such as 86 and remainingp-doped fiber regions 88. Electrical contact with the p-type cores ofthe fibers can be provided by the contact between the fibers and theconducting substrate. Electrical contact with the n-type outer regionsof the fibers can be provided by evaporating a conducting film, shown at90 in FIG. 3D. Other methods include contacting the distal ends of thefibers with a plane, transparent electrode, such as a flexible filmhaving a conducting surface region, providing wires, capacitive orinductive coupling, or other methods.

FIG. 4 shows in cross-section a photovoltaic device shown generally at80 comprising a first electrode 82, semiconductor slab 84, the slabhaving p-doped region 84 a and n-doped region 84 b so as to form a p-njunction 84 c, the slab having a surface 86, electrode 88, plurality offibers disposed on surface 86, such as fiber 90, and electricalconnectors 92 and 94.

In this example, the fibers can be attached to the surface 86 by aflocking technique. The surface 86 may be coated, at least in part, witha flock adhesive layer 96 or protective layer 98 before the fibers areattached.

In certain embodiments of the device shown in FIG. 3, the fibers andflock adhesive are substantially transparent to radiation of interest.In the case of a silicon based photovoltaic device, radiation ofinterest comprises visible and IR wavelengths. The fibers may compriseoptical fibers (such as glass fibers or polymer fibers), or other fiberstransparent to wavelengths within the range of wavelengths that caninduce a photovoltaic effect within a semiconductor material.

In other embodiments, the fibers can be doped with, be coated with, orotherwise support, fluorescent materials. These fluorescent materialsmay be advantageously used to generate a fluorescent wavelength to whicha photovoltaic element (such as a semiconductor slab, or photovoltaiclayer) is relatively sensitive to, using an excitation wavelength atwhich the photovoltaic element is less sensitive. For example,fluorescent dyes may be advantageously provided which produce redfluorescence from blue excitation radiation, as a conventional siliconphotovoltaic device is more sensitive to red light than to blue light.The plurality of fibers may comprise solid rods, tubes, loops, curvestructures, or other forms. U.S. Pat. No. 5,816,238 to Burns et al., thecontents of which are incorporated herein by reference, disclosessuitable fluorescent dyes, including thioxanthone, peryline imide,and/or thioindigoid compounds.

For example, an improved solar cell may comprise a conventional solarcell, onto which a flocked layer of polymer fibers are deposited. Aconventional amorphous silicon solar cell can be fabricated bydepositing an amorphous silicon layer onto a glass base, followed byin-diffusion of dopants. Regions of p-doping can be formed byintroducing boron atoms, and regions of n-doping can be formed byintroducing phosphorus. Doping is described in more detail in U.S. Pat.No. 4,322,571. A p-n junction is created, and electrodes connected tothe front and back of the cell. An improvement comprises coating thefront (light exposed) surface of the cell with an adhesive layer, thenusing conventional flocking methods to coat the front surface withfibers.

In a another embodiment, a photodetector, such as disclosed in U.S. Pat.Nos. 4,663,118 or 5,119,156, can comprise a flocked fiber layer on thelight entry surface of the photodetector. An improved photodetector maybe fabricated by depositing a plurality of fibers onto a light receivingsurface by a flocking method. The fibers may comprise light absorbingchemicals (dyes) and structures, fluorescent materials, phosphors, orother spectrum shifting or spectrum modifying components so as toincrease sensitivity or reject an unwanted wavelenght.

FIG. 5 shows a cross-section 100 of an improved solar collector, in theform of a fiber-coated pipe, for heating of a fluid such as water,comprising a tube 102, having an inside surface enclosing a passageway104 through which a fluid may pass, and an outer surface having disposedthereon a plurality of fibers 106.

The fibers can be coated onto the outer surface of the tube by aflocking technique. The tube may be rotated during a flocking process tohelp obtain a more uniform coating or radial distribution of fibers.Alternatively, the fibers can be disposed only on parts of the outsidesurface of the tube which will be exposed to light. In otherembodiments, the fibers may cover only a portion of the outer surface ofthe tube, and may be substantially parallel. The outer surface of thetube may be coated with a light absorbing surface, such as black paint.The flock adhesive may be light absorbing.

In an alternative embodiment, the outer surface of a tube is wrappedwith a flexible coating having a plurality of fibers extending radiallyoutwards. The flexible coating may be a black flocked fabric.

The fibers provide a number of advantages, such as improved solar energyabsorption, reduced convection cooling. The fibers may comprise, forexample, a plastic containing a light-absorbing chemical. The lightabsorbing chemical may be evenly distributed through the fiber, or maybe concentrated near the flocked surface. The fibers may be solid rods,tubes, or another form.

FIG. 6 shows an improved photothermal fluid heating system 120comprising a fiber coated pipe 122 such as described above in relationto FIG. 5. A sinuous tube 128 has a central aperture 126, through whicha fluid passes, or can be contained, and a plurality of radiallyextending fibers (124) coating the outside surface of the tube. Forexample, water may be continuously pumped through the system, which maybe mounted on the roof of a house. A transparent protective layer, suchas glass, may cover the fiber coated tube. The fluid heating system ofFIG. 6 can also be advantageously used for water sterilization, byallowing contained water to achieve an elevated temperature beforerelease from the system.

FIG. 7 illustrates, in cross-section, an optoelectronic devicecomprising a substrate 140 coated with a plurality of electricallyconducting fibers, such as fiber 142, an electroluminescent layer 144, aconducting layer 146, and a separating layer 148. The separating layermay be an adhesive layer, insulating layer, or a conducting layer, andin other embodiments may be omitted.

The conducting fibers may comprise graphite, metal, or other conductingmaterial. The electroluminescent layer may comprise a polymer,transition metal complex, or other electroluminescent material. Theconducting layer is preferably transparent at the luminescentwavelength, and may comprise a conducting oxide, such as indium tinoxide.

In other embodiments, an optoelectronic device can comprise a substratesurface supporting a plurality of fibers, a first layer covering atleast part of the substrate surface and fiber surfaces, and a secondlayer covering at least part of the first layer. For example, the secondlayer can comprise a metal film, conducting oxide, or other material,and the first layer can comprise a light emitting material such as alight emitting polymer. An advantage of this device configuration is anincrease radiant area. In another embodiment, the second layer comprisesa photovoltaic material which provides an electrical potential onillumination by photons. An improved solar cell, having improved lightabsorption efficiency, may have this configuration. Electrical contactsmay be provided to the first layer, second layer, or to an additionalconducting layer which may be provided to cover or otherwise be inelectrical communication with the second layer.

FIG. 8 shows a fiber 160 in cross-section comprising an electricallyconducting core 162 surrounded by an electroluminescent layer 164 and anouter conducting film 166. The core is aligned with an electrode 174 bysurface texture of the substrate 170, in this example in the form of adepression 168. The depression may take several forms, such asdish-shaped or the form of a trench. An insulating layer 172 is disposedon the substrate. The distal end of the fiber can also be coated with aninsulating layer 174. A conducting layer 176 is provided, which forms anelectrical contact with the conducting film 166. Provision of anelectric current between the electrode 174 and the conducting layer 176induces electroluminescence from the electroluminescent layer 164.

For example, the fiber core 162 may be metal or conducting polymer. Theelectroluminescent layer may be an electroluminescent polymer ormonomer. The conducting film 166 may be a transparent electrode or atransparent conducting polymer, metal film, other conducting polymer,semiconductor, oxide film, or other material. In other embodiments, thefibers may comprise a photovoltaic material or structure.

FIG. 9 shows a plurality of fibers supported on a surface, selectivelyilluminated by a laser. The system comprise a laser 180, a beam steerer182, a substrate, substantially transparent to laser radiation, 184, afiber 186, a fiber 188, and laser blocking (e.g. absorbing orreflecting) layers 190, 188, and 194. The beam steering device allowssingle fibers, or groups of fibers, to be selectively irradiated.Focusing lenses or other optical elements can be provided asadvantageous.

For example, optical fibers can be doped with luminescent dyes, andflocked onto a substrate. For example, a single long fiber can be dopedand then chopped into shorted segments for flocking. A scanned laserbeam can be used to excite luminescence from the irradiated fibers fordisplay applications. For example, the fibers and laser can be the sameside of the substrate, and radiation emitted through the substrate,which acts as a screen. Alternatively, the laser can be on the oppositeside of the substrate from the fiber array. The substrate should betransparent at the appropriate wavelengths. For example, fiberscontaining red, green, and blue emitting luminescent dyes can bedistributed in predetermined patterns on a substrate, for example usingsequential patterned deposition of a flock adhesive, each patternedadhesive deposition being followed by flocking of color emitting fibers.

In other embodiments, the fibers may be long enough so that conversionof laser excitation wavelengths to fluorescence wavelengths issubstantially complete. The blocking layers 188 and 194 may be omitted.If a blue laser is used, red and green fluorescing fibers can be used,along with clear fibers (or non fiber-coated regions) for providing bluecolor to a display. Here, the term fluorescence includesphosphorescence. Beam steering devices are well known in the art, andneed not be described in detail here. A beam steering device accepts anelectrical signal and modifies the path of a beam in a manner correlatedwith the signal content, e.g. using photorefractive, mechanical, orother methods known in the art.

FIG. 10 shows an optoelectronic device, in cross-section, comprisingfirst substrate 200, supporting a first plurality of fibers such as 202,in opposition to a second substrate 206, supporting a second pluralityof fibers such as 204. The double headed arrow labeled d represents thegap thickness (d) between the two substrates. Subtrates may be sized andshaped appropriate for device configuration, such as a single lightemitting lamp, display, photovoltaic roof covering, photodetector, orother application.

In one embodiment, fiber 202 comprises an electroluminescent layercoated onto a conducting core. For example, fiber 202 may comprise ametal core coated on the side surface of the fiber with anelectroluminescent polymer, the metal core being in electrical contactwith a lower electrode on the lower substrate. The terms upper and lowerare used for convenience in relation to the Figure, and are notlimiting. Fiber 204 is a conducting fiber, such as a metal fiber, inelectrical contact with an upper electrode on the upper substrate.Application of an alternating voltage between the upper and lowerelectrodes induces electroluminescence from fiber 202, and similarfibers. All fibers on the lower substrate may comprise anelectroluminescent layer, and all fibers on the upper substrate may beconducting fibers.

In other embodiments, there is a mixture of fiber types on upper andlower substrates. Regions of electroluminescent fibers, which may be ofa chosen color emission, may be selectively energized using electricalconductors on top and bottom substrates. For example, transparentelectrode stripes, such as indium tin oxide, may be provided on upperand/or lower substrates. Transparent electrodes may be provided on onesubstrate, and non-transparent electrodes provided on the other. The gapthickness d can be set at greater than the conducting fiber lengths, forexample using spacer elements, or including non-conducting fibers ofslightly greater length into the mixture of flocked fibers. Fibers maybe energized by alternating electrical fields even without a directconductive path. In photovoltaic device embodiments, at least somefibers comprise a photovoltaic material.

In one embodiment, the fibers comprise an electroluminescent material,which emits light if an electric potential is applied to the fibers.Areas of fiber-coated substrate can be selectively energized, forexample by using a stripe pattern of conductors on top and/or bottomsubstrates, for example crossed stripe patterns of conducting,transparent electrode materials such as indium tin oxide.

FIG. 11 shows a lower substrate 220 supporting fibers 222. The distalend of the fibers can be made to contact the upper substrate 224 byreducing the gap thickness, d, for example by mechanically forcing thesubstrates together.

In another embodiment, one substrate supports n-doped semiconductorfibers, the other substrate supports p-doped semiconductor fibers.Semiconductor p-n junctions are formed where fibers supported byopposing substrates are in contact. Lateral motion of substrates may beprovided to facilitate contact between. In this embodiment, the gapthickness can be greater than the fiber length.

The gap between opposing substrates may be evacuated, filled with inertgas such as a rare gas or nitrogen, or filled with a transparentinsulator.

FIG. 12 shows a number of fibers 246 flocked onto a textured surface 248of substrate 240. A flock adhesive layer 242 holds the fibers in place.A conducting film 244 provides electrical contact with the fiber edges.

In one embodiment, the fibers comprise p-doped silicon, and thesubstrate comprises n-doped silicon. A p-n semiconductor junction isformed at the interface between the fibers and the substrate surface.(As stated elsewhere, in relation to all examples, the p-doped regionsand n-doped regions can be reversed.)

In another embodiment, the fibers and substrate are initially p-dopedsilicon, then the exposed areas of fibers are exposed to n-dopantdiffusion (for example, by exposure to a gaseous phosphorus compoundsuch as phosphine) so as to form a p-n junction near the exposed surfaceof the fibers. This n-doping may occur after flocking but beforedeposition of the conducting film.

In a further embodiment, the substrate 240 comprises a silicon filmhaving a p-n junction, and the fibers are transparent in part of theIR-visible light spectrum so as to guide light to the surface of thesilicon film. In this case, the conducting film may be transparent. Aconducting flock adhesive may be advantageously used.

FIG. 13 shows a conducting substrate 260, having a number of flockedfibers 264 held in place by a flock adhesive layer 262. A second layerof flocked fibers, such as 266, are then deposited. An adhesive (notshown) may be used to hold the second fiber layer in place. A conductingfilm 268, such as a metal film, metal coated flexible film, or otherconductor, is then used to make electrical contact with the secondlayer. For example, the first layer of fibers 264 may be p-dopedsemiconductor, and the second layer 266 may be an n-doped semiconductor,so as to create a p-n junction at the contact between the two fiberlayers. In other embodiments, additional layers may be deposited, forexample so as to obtain higher potential photovoltaic devices. Devicesmay comprise uniformly layered, non-uniform, or dendritic fiberstructures.

FIG. 14 shows, in cross-section, an electrically conducting substrate280, supporting a plurality of electrically conducting fibers 284 heldin place by a flock adhesive layer 282. The fibers, which may comprise aconducting core, such as metal, are coated with an electroluminescentcoating 288. The coating 288 can be deposited after the fibers aredisposed on the substrate, for example by vapor deposition, dipping intoa solution, evaporation, sputtering, sublimation, or other depositionmethod, or the coating may be formed before deposition of the fibers.The coating may comprise a polymer such as P3HT(poly(3-hexylthiophene)), or a blend of P3HT and CdSe, wherein CdSe(cadmium selenide) particles or nanorods are dispersed through the P3HTlayer. Such a blend is known in the art. A conducting film 286 is formedso as to contact the outside of the electroluminescent coating, so thanan electric potential applied between film 286 and substrate 280 canexcite light emission from the coating. Separating layer 282 can be aninsulating layer, flock adhesive layer, conductive layer, light emittinglayer, photovoltaic layer, or can be omitted.

Light emission can obtained from electroluminescent materials (such aspolymers, metal complexes, and organic molecules) by providing suitableanode and cathode materials, as are known in the art. For example, asdisclosed in U.S. Pat. No. 6,461,885 to Lupo et al., anode materialsinclude indium tin oxide, polyaniline, fluorine-doped tin oxide, andgold, whereas cathode materials may comprise magnesium, aluminum,lithium, barium, calcium, or combinations thereof. Other anode andcathode materials are known in the art, the anode material having ahigher work function than the chosen cathode material. Further, chargecarrier transport layers, charge carrier blocking layers, and protectivelayers (such as to prevent oxidation) can be provided. For example, theconducting film 286 may be coated with an oxidation prevention layer,such as a glassy material, oxide layer, or other material.

Either the substrate 280 or the conducting film 286 can be the cathodefor the electroluminescent coating, depending on the choice of materialschosen for the substrate (or conducting substrate surface), theconducting core of the fibers, and the conducting film 286. Theconducting core of the fibers may also act as a cathode or anode,depending on materials selected. For example, the conducting core may besilver, and the conducting film may be ITO. Other combinations arepossible, as will be clear to those skilled in the art.

The conducting film 286 is in electrical communication with the fibers,and at least in part fills the spaces between the fibers. The conductingfilm can be provided by any deposition process, such as vapordeposition, vacuum deposition, sputtering, evaporation, solutioncoating, sublimation, and the like, or by other methods. (Thesedeposition methods can be used for other film deposition in otherembodiments). For example, a liquid (which may be a suspension,emulsion, or colloid) can be applied to the fiber coated surface, whichunder gravity and/or capillary forces migrates between the fibers. Theliquid then dries or otherwise solidifies, in ambient conditions, orunder heating and/or irradiation, to provide the conducting film.Suitable liquids are known in the art, for example liquid metals havinga suitable melting point (not so high as to damage the fibers, and notso low as to destabilize the device), also as described in U.S. Pat.Nos. 6,277,740 and 6,406,984, the contents of which are incorporatedherein by reference. Gaseous, liquid or solid components can be used toform conducting contacts with the fibers, for example as described inU.S. Pat. No. 6,406,984. Electric contacts (and other films such asconducting or insulating layers) may be formed by evaporation, othervapor deposition processes including plasma deposition, laser ablationdeposition, vacuum deposition, and the like, or deposition of chemicalprecursors (e.g. of conducting polymers such as polyaniline orpolyphenylenevinylene, the precursors of which may be polymerized orotherwise processed after deposition).

FIG. 15 illustrates an optoelectronic device comprising a substratehaving a conducting substrate surface 302, an adhesive layer 304covering at least part of the substrate surface 302, a plurality offibers such as fiber 306, a first layer 308, a second layer 310, a firstelectrical contact 312 in electrical communication with the first layer308, and a second electrical contact 314 in electrical communicationwith the first layer 310. The first and second layers can beelectrically conducting.

In an improved solar cell embodiment having the structure of FIG. 15,either the first or second layers comprises a blend of an organicsemiconductor with particles (such as nanoparticles or nanorods) of aninorganic semiconductor, for example a blend of electron acceptorparticles in a hole acceptor polymer film. Specific examples aredescribed below.

In an improved solar cell having the structure of FIG. 15, the firstlayer comprises a photovoltaic material (such as a blend of P3HT andcadmium selenide nanorods), the second layer comprises a conductingmaterial (such as PEDOT:PSS, (polyethylene dioxythiophene doped withpolystyrene sulphonate or equivalently polystyrene sulfonic acid, atransparent conducting film, the conducting substrate surface comprisesa metal film (such as an aluminum or copper film) or conducting oxidefilm. Blends of P3HT and cadmium selenide nanorods which may be used inembodiments of the present invention are described by Alivisatos andco-workers in Science, vol. 295, pp. 2425-7 (29 Mar. 2002).

In another embodiment of a solar cell having the structure of FIG. 15,the conducting substrate surface comprises indium tin oxide, the firstlayer comprises PEDOT:PSS, the second layer comprises a CdSe/P3HT blend,and an aluminum electrode may be deposited over at least part of thesecond layer.

A further embodiment comprises a substrate, a plurality of fibersdisposed on the substrate, a first layer disposed on at least part ofthe substrate surface and fiber surfaces, comprising a light emittingmaterial such as poly (p-phenylenevinylene) or other light emittingpolymer, and a second layer, disposed on at least part of the firstlayer, comprising a conducting material for example, a conductingpolymer, a metal film, conducting oxide film, a hole transport layer,PEDOT:PSS, or other conducting material. Alternatively, the second layermay comprise PPV or other light emitting polymer or light emittingmaterial, the first layer may be a hole transport layer or otherconducting film, and an additional third conducting layer providedcovering at least part of the second layer. Electrical contacts,including patterned conducting structures on the substrate, or patternedconducting layers, can be provided as known in the art, for example asdescribed in U.S. Pat. No. 6,462,469 to Young, the contents of which areincorporated herein by reference.

In other embodiments, fibers may comprise PPV or other light emittingpolymer, the first layer may comprise PEDOT:PSS or other conductingfilm, and the second layer may be omitted, or comprise a conductingelectrode material.

OTHER EMBODIMENTS

In other embodiments, a plurality of fibers, oriented with respect to asurface, can be used to align a liquid crystal layer. The aligned liquidcrystal film can be used as an electro-optical shutter to modulate lightemission from the fiber, or other light source. Appropriate combinationsof electric field directions, fluid flow direction (with respect topneumatic flocking) and surface microrelief can be used to provide anoblique alignment of fibers on the surface, which can provide highpretilt or bistable alignment of the liquid crystal layer.

In general, with reference to above described embodiments, a conductingsubstrate surface may comprise a metal (such as aluminum, copper, gold,silver, or some alloy or multilayer), a semiconductor, a dopedsemiconductor, a conducting polymer, or other conductor. The fibers maycomprise a metal, conducting polymer, doped semiconductor, or otherconductor. The first layer may comprise a conducting polymer (such aspoly(p-phenylene vinylene) or derivative thereof), a hole acceptingpolymer (such as poly(3-hexylthiophene, P3HT), a blend of cadmiumselenide particles and P3HT), or other material.

Flocked surfaces can also be used to create membrane electrodes, forexample, for use in fuel cells. In this case, the fibers may comprisemetal coated perylene red, for example as disclosed in U.S. Pat. No.6,425,993, the contents of which are incorporated herein by reference.Fabrication of conducting coated fibers, and other shapes, is disclosedby U.S. Pat. No. 6,395,149 to Palmgren, the contents of which areincorporated herein by reference.

Flocked conducting fibers can be used to provide an improved electronemitter. For example, conducting fibers (such as fullerene tubes,graphite fibers, metal fibers, and the like) can be flocked onto aconducting surface (such as a metal, conducting polymer, dopedsemiconductor, and the like).

Fibers may comprise glass, polymers (such as rayon, nylon, polyesters,acrylates, terephthalates, polypropylene, polyethylene, semiconductingpolymers), metal, metal oxide, non metals (such as silicon), oxides ofnon-metals, carbides, and nitrides. Fibers may be: conducting,semiconducting, or insulating; metallic, non-metallic, or semi-metal;formed from a single compound or a mixture of compounds; crystalline,glassy, liquid crystalline, or amorphous; uniform composition, gradedcomposition, or comprise multilayer structures such as concentricregions.

Fibers may be conventionally sized in relation to conventional fabricuse, for example having a length of approximately 0.76 mm, or may have alength in the range 0.1-10 mm, for example 0.2-5 mm, for example 0.2-3mm. However, fibers may be shorter or longer than this. For example,longer fluorophor-doped fibers may increase the fluorescence intensityproduced. Fibers may be coated with a protective film before or afterflocking. A bulk sample of polymer may be doped with a fluorescentmaterial before being drawn into long fibers, which may then besubsequently chopped into shorter length fibers. Alternatively, fibersof the final desired length can be vat dyed, or other additive added tothe fiber. Fibers may be created by chopping a much longer length intothe length desired, growth in micelles, or any other appropriatetechniques. Fiber cross sections can be circular, oval, elliptical,square, polygonal, hollow, contain multiple apertures, or be of someother form.

Substrate surfaces may be plane, concave, convex, undulating, orotherwise structured. For example, a concave or convex substrate surfacemay be advantageous for photovoltaic devices. An improved optoelectronicdevice, such as a light emitting device, may comprise a source ofexcitation radiation surrounded, at least in part, by a substrate havinga convex surface coated with a plurality of fibers, the fiberscontaining a fluorescent material. The fibers may be radially disposedin relation to the excitation source, and either the same side of thesubstrate as the excitation source or an opposite side.

Solar cell embodiments may be illuminated from the fiber side of thesubstrate surface. If the substrate is transparent, illumination may befrom the opposite side of the substrate as the fibers.

Substrates may be rigid or flexible, and may comprise a woven fabric.For example, embodiments of the present invention include wearablephotovoltaic cells, for example for powering a personal computer, andwearable highly fluorescent fabrics.

Substrates may include light absorbing, fluorescent, or reflectivelayers. For example, a fluorescent fabric may comprise fluorescent dyedoped fibers flocked onto a flexible substrate having a reflective layerserving to reflect back incident light and/or fluorescence.

Examples have been described in relation to flocking methods. However,other techniques can be used to cover a surface with fiber equivalents,such as cutting loops, creation of surface textures (such asprotrusions, ridges, holes, and the like), and other surfacemodifications. Methods which may be used include etching (including wetetching and dry etching methods), scribing, laser ablation, vapordeposition, methods adapted from scanning microscopy, manual placement,crystal growth techniques, localized heating, localized fiber pulling,stamping, and the like.

Devices have been described having p-doped and n-doped semiconductorregions. As will be clear to those skilled in the art, it may bepossible to reverse the doping pattern (i.e. replace n-doped regionswith p-doped regions, and vice-versa). Electric potentials, currentflows, and the like may also be reversed. Semiconductor p-n junctionsmay be formed between p-doped and n-doped regions of the same chemicalcomposition, or may be semiconductor heterojunctions. In otherembodiments, a junction between a hole accepting compound and anelectron-accepting compound can be provided instead of, or in additionto, a p-n junction, for example a junction between cadmium selenide andpoly(3-hexylthiophene).

Light emitting devices fabricated according to the present invention mayfurther comprise drive electronics, segmented, pixilated or otherwisepatterned electrodes and/or light emitting layers, protective layers,reflective films, lenses, polarizers, optical filters, other opticalcomponents, power supplies, data communication interfaces, hole blockinglayers or electron blocking layers proximate to light emittingmaterials, thin film transistor driving mechanisms, or other display orlight emitting device components known in the art.

Solar cells fabricated according to the present invention may furthercomprise charge storage devices (such as batteries or capacitors),lenses or mirrors to direct sunlight onto operable regions of thedevice, UV filters for reduction of degradation, and the like.

Fibers may be excited by various methods, or combination of methods, toproduce light emission. For example, the fibers may be illuminated withelectromagnetic radiation (such as UV, visible, IR, microwave, radiowaves, or x-ray radiation), which also includes ambient light, sunlight,lasers, and the like. Fibers may contain phosphors, for example toprolong light emission time after excitation. The phosphors may providea prolonged light emission after excitation has ceased, or may provideexcitation radiation after external excitation has ceased.

An organic electroluminescent devices may comprise an anode, a holetransporting layer deposited on the anode, an electron transportinglayer, and a cathode, wherein the hole transporting layer or electrontransporting layer may comprise a light emitting material.Conventionally, co-planar films are used. In embodiments of the presentinvention, light emitting materials may be used to form fibers, withother necessary layers deposited on the fibers or on the substratesupporting the fibers. Light emitting materials may also be used to formlayers supported by flocked fibers, so as to increase light emissionarea. Another device configuration comprises a multilayer having ananode, a hole transporting layer, a light emitting material, and acathode. In embodiments of the present invention, fibers or layersdeposited thereon may comprise the light emitting material.

Fibers may be excited to electrical potentials, direct or alternating,for example through electrical contacts, proximity to electrodes (e.g.through capacitive coupling, inductive coupling), electronic discharges,static fields, and the like. Fibers may also be excited by ultrasound,triboluminescent effects, or other mechanical energy input,radioactivity, or heat.

Elements of each described embodiment, and other configurations, may becombined in other ways as will be clear to those skilled in the art.Examples given are not intended to be limiting. Other embodiments willbe clear to those skilled in the arts.

1-22. (canceled)
 23. A photovoltaic device, comprising: a semiconductormaterial comprising a p-doped region and an n-doped region, a p-nsemiconductor junction between the p-doped region and the n-dopedregion, wherein an electrical potential is developed between the p-dopedregion and the n-doped region on illumination of a surface of thesemiconductor material; an electrical contact to the n-doped region; anelectrical contact to the p-doped region; and a plurality of fibersrandomly distributed across the surface of the semiconductor material.24. The device of claim 23, wherein the fibers comprise a polymer. 25.The device of claim 23, wherein the semiconductor material comprisessilicon.
 26. The device of claim 23, wherein the semiconductor materialcomprises silicon, and the fibers comprise a polymer.
 27. The device ofclaim 23, wherein the fibers are disposed substantially orthogonal tothe surface of the semiconductor material.
 28. The device of claim 23,wherein the fibers comprise a fluorescent material.
 29. The device ofclaim 23, wherein the fibers comprise a light absorbing material. 30.The device of claim 23, wherein the surface of the semiconductormaterial further supports a protective layer, the fibers being disposedon the protective layer.
 31. The device of claim 23, wherein the surfaceof the semiconductor material further supports an adhesive layer, theadhesive layer holding the fibers proximate to the surface of thesemiconductor material.
 32. A photothermal system, comprising: a tubehaving an outer surface and an aperture in which a fluid can be located;a layer of adhesive on the outer surface of the tube; and a plurality offibers disposed on the outer surface of the tube, held in place by thelayer of adhesive.
 33. The system of claim 32 further comprising a lightabsorbing layer on the outer surface of the tube.
 34. The system ofclaim 32, wherein the fibers contain a light absorbing material.
 35. Thesystem of claim 32, wherein the tube has a sinuous form.
 36. The systemof claim 32, wherein water is pumped through the aperture.
 37. Thesystem of claim 32, wherein the tube is mounted on a surface exposed tosunlight, and protected from mechanical damage by a transparent sheetmounted above the tube.
 38. A light emitting system, comprising: asubstrate having a substrate surface; a plurality of fibers supportedheld on the substrate surface by a layer of adhesive; a source ofenergy, wherein the source of energy induces a light emission from thefibers.
 39. The system of claim 38, wherein the source of energycomprises a laser.
 40. The system of claim 38, wherein the source ofenergy comprises an electric potential.
 41. The system of claim 38,wherein the fibers comprise an electroluminescent material. 42-43.(canceled)